In order to solve the interference caused by random fluctuations and intermittence of wind and solar power on power generation systems, this paper designs an off-grid wind and solar complementary pumping system based on the three-port converter. The wind and photovoltaic power generation systems are used as input power supply of the system, and asynchronous motor pumping is used as load end of the system. Firstly, the mathematical models of wind power generation system, photovoltaic power generation system and pumping system are established respectively, and the control strategies of wind-solar alternate switching and simultaneous switching are studied. Among them, an optimized variable-step conductance increment method is employed on the photovoltaic side, and vector control based on rotor flux orientation is applied to the permanent magnet synchronous motor and asynchronous motor. The DC bus voltage is regulated by the outer loop control of the asynchronous motor voltage, and the system power is controlled by the outer loop speed control of the permanent magnet synchronous motor. The topology of the three-port converter varies with wind-solar switching. This compensates for the deficiency of the wind and solar power generation systems, ensures the stability of the system operation, and achieves the objective of integrating wind and solar pumping with energy conversion. Finally, a simulation model of the off-grid three-port wind and solar complementary pumping system is built using Matlab/Simulink software. The results validate the rationality of the model design and the correctness and feasibility of the switching strategy during system operation.